After thinking about my next construction project, I decided to have a go at building from scratch the old P.W. Dart Double Sideband Topband Transmitter, which came from Practical Wireless in Nov / Dec 1983. The components were all easy to find and I already had most of the small components. This will make a nice complement to the RAT5 Receiver and Multi-Rock II VFO.
I used the PCB designs in the magazine and set about making my own boards. There would be three boards…audio board, mixer board and PA board. Later I decided to build an extra board with an ‘RF sniffer’ connected to an LED so that I could monitor the output. The circuit uses a diode mixer SBL-1x which is similar to the MD108 that I used when I built a transceiver using SL600 chips many years ago.
With the boards now completed, I bought a matching case to the RAT5 and Multi-Rock VFO II to mount the boards and build up the wiring and controls. I took the PA tuning capacitor from an old ATU that was given to me. I bought a CB microphone from Maplin to use with the transmitter.
The completed P.W. Dart
When I tested the transmitter I had some RF feedback, but managed to cure this by adding more decoupling capacitors on the audio and mixer boards as well as making sure that everything was properly earthed including the screened cables. I have been getting good reports locally even though the output of the transmitter is just 2w. I can also see my transmissions on G4HYG’s on-line SDR Receiver. I have found this very useful to monitor my transmissions and set up the audio and PA output.
This is the first project for many years that I have built from scratch, which included making the printed circuit boards.